But don't expect a quick fix. Laser weapons have come a long way in the past decade, but they're still years away from defending against threats ranging from North Korean long-range nuclear missiles to short-range explosive-laden drones launched by ISIS.

The Pentagon has worried about nuclear strikes by "rogue states" since the end of the Cold War. In 1996 the Air Force began work on the Airborne Laser, a plan to put a megawatt-class chemically powered laser in a Boeing 747 that could patrol near potential nuclear threats, which then included Iran and Iraq as well as North Korea. In case of a launch, the laser would fire to catch the rocket at its most vulnerable stage, as it was boosting out of the atmosphere. Two massive ground-based lasers had already demonstrated megawatt output, and the Airborne Laser used a more advanced chemical system that promised to make a better weapon system.

The Airborne Laser finally shot down target missiles in 2010, years late and far above its original budget, but that was too little and too late to avoid cancellation. The laser hadn't delivered enough power far enough to shoot down a missile at the desired range. Logistics experts also found the practice of shoehorning dangerous chemical fuels within a laser into an airplane to be an insoluble problem.

Illustration: Missile Defense Agency
The scrapped Airborne Laser was a complex weapons system packed into a Boeing 747.

When asked why he cancelled the program, Secretary of Defense Robert Gates said he knew nobody in the Pentagon "who thinks that this program should, or would, ever be operationally deployed. The reality is that you would need a laser something like 20 to 30 times more powerful than the chemical laser in the plane right now to be able to get any distance from the launch site to fire." After a final series of tests, the Airborne Laser was scrapped in 2014.

The new generation of laser weapons are electrically powered solid-state types which can run on power from diesel generators. The Missile Defense Agency is considering that technology for laser-armed drones to defend against North Korean missiles. These drones would be much smaller than a 747, and carry a payload of 5,700 kilograms at 63,000 feet, compared to a 747's payload of over 200,000 kilograms at 40,000 feet. The beam should go further at the higher altitude, but the planned prototype wouldn't be ready until 2023.

Ground-based solid-state lasers have scored a series of successes. Last week, a 30-kilowatt Lockheed Martin ground-based system called ATHENA shot down five drones at the White Sands Missile Range. Earlier this year, Lockheed completed a 60-kilowatt version of the laser for the Army Space and Missile Defense Command in Huntsville, Ala. to test in a military truck. The Navy has tested a 30-kilowatt laser on the USS Ponce and plans ship-based tests of a 60-kilowatt laser.

But those lasers are testbeds, not weapons ready for field use. After testing several lasers with other anti-drone weapons at White Sands, the Joint Improvised-Threat Defeat Organization summed up the results as: "Bottom line: Most technologies still immature." They had hopes for improvement, but said "threat targets were very resilient against damage."

Shooting down enemy drones, such as those used by ISIS, with laser-equipped drones requires identifying a target drone’s most vulnerable spots, says Philip Coyle, Senior Science Fellow at The Center for Arms Control and Non-Proliferation. "Just hitting the fuselage of the drone might not do much damage. Much of the laser energy would bounce off, and even if the laser was powerful enough to burn a hole, the drone might be able to continue flying." The engine or spots on the wing or tail might be more vulnerable. But that would vary among drones, and the Army would have to figure out what drones ISIS uses and where they are vulnerable.

"Another problem is that these laser defense systems are expensive, and we can’t afford to sprinkle them over a large area," adds Coyle. A laser's lethal range depends on its power and the vulnerability of potential targets, but is likely to be limited to a few miles.

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